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        // console.log(NaN, typeof NaN);
        // console.log(0 / 0 ,6 / 0,-6/0);
        // console.log(Math.sqrt(-1));
        // console.log("abc" - 10);
        // console.log(undefined + 5);
        // console.log(parseInt("hello"));
        const a = 0 / 0;
        const b = parseInt("hello");
        if(Number.isNaN(parseInt("hello"))) {
            console.log("不是一个数字，不能继续计算了");
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